I did layering for a number of years, and when I got my new horse I just had problems with it. No matter what kind of liner (fleece or nylon) I used it would always shift on her. I always used 2 sets of leg straps, and it still shifted so I had to change my blanketing plan this year.
My mare doesn’t grow a great coat, and it take until December for her to fully get what little she does grow. She lives outside 24/7 unless the weather gets really bad like snowing bad and the temperature is going to drop or something like that. She does have a lean to that she can go into. Anyways during the 40/50 degree weather during the day I use a sheet no fill. 20/30 degree weather I will use a light weight 80 to 100 fill depending on what brand of blanket you use. Teens and single digits I will put on a medium weight usually around 220 fill. And below zero I will put on a heavy weight with a hood. The system that I have in place she seems to stay comfortable.
I will take into rain/snow and the wind chill (I check weather everyday) If it says its going to be in the low 40s but really windy and rainy I’ll put on the light weight. Same with if it’s the 20s, and the wind chill is bad I’ll put on the medium weight. I am on a self care board, so I’m able to change my blankets more. I hope this helps some.